This invention relates to optical lens zoom systems, and more particularly to an improved guiding mechanism for controlling the moving parts or elements in such a lens system. It has long been customary in zoom lens systems of the type described, to employ ball bearing rollers for guiding moving parts of a zoom lens within the lens barrel. It has also been customary heretofore to employ in such lens barrel various parts which are mounted for sliding movement relative to each other to effect variation in magnification of an observed object. Lenses of the type described are frequently employed in motion picture photography and television broadcasting, which usually demand the highest of image quality. Typically such a zoom lens system includes in the lens barrel two moveable sets of lenses, the first or forward group of lenses being disposed to vary the angle of view, the second set being operative to restore the focus upon adjustment of the first group.
Among the disadvantages or prior such zoom lenses has been the difficulty encountered in accurately, and in some instances quietly, moving the respective sets of lenses. Such prior art devices also require a nearly polished finish on the inner bore wall of the lens barrel, thus contributing significantly to the manufacturing costs of the lens systems.
Accordingly, it is an object of this invention to provide an improved optical zoom lens system of the type described in which the lenses can be moved accurately and with precision not heretofore available.
Still another object of this invention is to provide an improved guiding mechanism for moving parts of an optical zoom lens system of the type described, which mechanism is easier to manufacture and is longer lasting than prior such guiding mechanisms.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.
In typical metrological setups, mechanical bearings are used to support and actuate a zoom lens. However, mechanical shift of the zoom components can generate an optical images shift that is an error of measurement in the optical measuring machine. Various designs of mechanical bearings have been made to attempt to overcome this problem, but the shift and resultant error remain. For example, U.S. Pat. No. 6,507,705 to Kasha, the disclosure of which is hereby incorporated by reference in its entirety, discloses one of the most accurate guiding mechanisms available for moving parts in a zoom lens system. The tubular barrel of a zoom lens mechanism has secured in the bore thereof a plurality (three in the embodiment illustrated) of elongate, circular rods which are secure to the inner peripheral surface of the barrel to extend axially thereof and in angularly spaced relation to each other. Each of a plurality of cylindrically shaped lens housings are mounted coaxially in the bore of the barrel for axial adjustment therein by means of a plurality of sets of rollers on each housing, each of which sets on each housing has rolling, point engagement with a different one of the rails. One set of rollers on each housing is urged resiliently into rolling engagement with the associated rail, while the other two sets of rollers in such housing are rotatable about axes which are fixed with respect to the associated housing. Each housing has thereon a pin which projects through a slot in the barrel and into a cam groove formed in one of two different zoom or camming rings which are rotatably mounted on the barrel. The rolling point contact between the rails and the rollers on the housing, significantly improve the accuracy and life of the mechanism. However, even this system can suffer measurement error when mechanical shift of its mechanical bearings occurs.
Embodiments offer an alternative to the mechanical bearings of the prior art. Air bearings are used in embodiments to guide a zoom lens, eliminating mechanical bearings and the related mechanical and image shift. The air bearings have higher stiffness than the mechanical bearings of the prior art, minimizing the shift of moving components in the lens system. Thus, the zoom lens system guided by an air bearing system results in greater accuracy, overcoming the problems of the prior art.